The invention relates to a device comprising two bodies which are disposed coaxially with respect to a translation axis and comprising a suspension means via which at least one of the bodies is movable with respect to the other body along the translation axis.
Such a device is known from U.S. Pat. No. 4,829,582. Said Patent Specification discloses a loudspeaker having a conical diaphragm connected to a chassis by a suspension means comprising an axially resilient annular centering element. The diaphragm, which has a main axis, has a coil former with a coil secured to it for cooperation with a magnet system via an air gap, the magnet system being secured to the chassis. The centering element, which is made of, for example, a textile fabric, exhibits an undulating pattern viewed in a radial cross-section and extends substantially perpendicularly to the main axis of the diaphragm. The centering element provides a certain axial spring stiffness and such a transverse stiffness that in operation the coil moves centrically in the air gap. A disadvantage of the known loudspeaker is that an extended centering element of comparatively large diameter is necessary in order to allow a comparatively large axial excursion with a satisfactory linearity of the coil to be achieved. In applications where only a limited space is available the known centering element does not allow a comparatively large axial excursion of the element of the diaphragm and hence of the coil to be obtained while the requirements as regards linearity and mechanical stability are fulfilled.
It is an object of the invention to provide a device of the type defined in the opening paragraph, in which the suspension means requires a comparatively small space but allows comparatively large and accurately defined axial excursions of the one body with respect to the other body.
To this end, the device in accordance with the invention is characterized in that the suspension means comprises a set of at least three blade spring elements which are positioned around the translation axis, which blade spring elements each comprise two blade springs which are inclined with respect to a plane oriented perpendicularly to the translation axis, the blade springs of each blade spring element each having two peripheral portions which each extend parallel to the plane which is oriented perpendicularly to the translation axis, one of the blade springs being connected to the one body near one of its peripheral portions and the other blade spring being connected to the other body near one of its peripheral portions, while the blade springs of each blade spring element are interconnected near their other peripheral portions.
As compared with the centering element of the known device the basically frictionless suspension means, in which the blade spring elements are preferably disposed in a triangular or quadrangular arrangement, is of compact dimensions. The shape of the blade spring elements, which is in fact a saddle-roof shape, in combination with the arrangement of the blade spring elements relative to one another, guarantee an accurate linear guidance of the two bodies with respect to one another. The axial spring stiffness of the suspension means used is dictated by the dimensions of the blade spring elements and the flexural stiffness of the blade springs. The blade springs can be made of spring materials which are know per se, such as spring steel, phosphor bronze or suitable plastics, such as a reinforced polycarbonate.
An embodiment of the device in accordance with the invention is characterized in that at their adjacent peripheral portions the blade springs of each blade spring element are interconnected in a non-deformable fashion. In this embodiment, in which the connection between the blade springs of a blade spring element is stiff, the angle formed by each pair of blade springs of each blade spring element is in principle constant, which is favorable in order to preclude material fatigue, particularly at the location of the interconnection.
For similar reasons an embodiment is preferably characterized as defined in Claim 3.
A practical embodiment of the device in accordance with the invention is characterized as defined in Claim 4. A suitable material is for example a plastic, such as polycarbonate, poly-acrylonitrile butadiene styrene, an injection-molding thermosetting material reinforced or non-reinforced with fibers, or mixtures of said plastics. Die-casting or casting metals such as aluminum are also suitable. Preferably, this embodiment is combined with the characteristic features defined in Claim 5. In production this can be implemented by means of an injection-molding machine. During the manufacture of the device the blade springs are then placed into the injection-molding machine and during injection-molding the peripheral portions are embedded in the bodies and the mutually rigid non-deformable connection is established. Preferably, the peripheral portions each have one or more perforations into which the embedding material extends in order to guarantee a connection which is reliable under any conditions.
A further practical embodiment is characterized in that as defined in Claim 7. Preferably, the bent blade spring is embedded near all peripheral portions of said blade springs for reasons already mentioned in the present description.
An alternative embodiment is characterized in that each blade spring element is an integral injection-molded product, preferably of a suitable plastic material, such as a reinforced or non-reinforced polycarbonate. In this embodiment the blade springs are comparatively thin and flexible and the peripheral portions are comparatively thick and non-deformable. If desired, the set of at least three blade spring elements can take the form of an integral injection-molded product.
An embodiment of the device in accordance with the invention is characterized in that the suspension means comprises a further set of at least three blade spring elements positioned around the translation axis, the two sets being axially spaced from one another. It is to be noted, for the sake of completeness, that the further set of a like type is identical to the first-mentioned set of blade spring elements. In such a device an optimum linear guidance of the bodies with respect to one another is achieved. In given applications it is preferred to arrange both sets in a mirror-inverted relationship with respect to a plane perpendicular to the translation axis, in such a manner that the asymmetric and non-linear behavior of one set is compensated for by the corresponding behavior of the other set.
The invention further relates to a loudspeaker device comprising a chassis and a diaphragm arrangement which is movable with respect to the chassis. In order to enable a compact loudspeaker device having a diaphragm arrangement capable of performing a comparatively large excursion the loudspeaker device in accordance with the invention comprises a device in accordance with the invention, the chassis forming or comprising the one body and the diaphragm arrangement forming or comprising the other body. Herein, a loudspeaker device is to be understood to mean both a loudspeaker and a passive radiator. In the case of a loudspeaker the term diaphragm arrangement covers both the diaphragm itself and an associated driving element, generally a driving coil. In operation, as is commonly known, this driving element cooperates with a further driving element, generally a permanent magnet, which is connected to the chassis.
It is to be noted that from U.S. Pat. No. 4,056,697 an arrangement is known for connecting a sound-reproducing movable diaphragm to a chassis or baffle. The arrangement includes two rigid non-deformable elongate planar members, which are connected to one another by means of a hinge, one of the members being connected to the diaphragm by means of a hinge and the other member being connected to the baffle by means of a hinge. The known arrangement has the disadvantage that during use the hinges are subjected to a substantial bending load, which may give rise to premature fatigue in the hinges. A further disadvantage is the limited excursion of the diaphragm with respect to the baffle allowed by the use of the suspension means.
The invention further relates to an actuator having a stationary part, a part which is translatable with respect to the stationary part, and an electromagnetic driving system. In order to enable a compact actuator having a translatable part whose excursion is comparatively large to be obtained, the actuator in accordance with the invention includes a device in accordance with the invention, the stationary part forming or comprising the one body and the translatable part forming or comprising the other body. The actuator in accordance with the invention is suitable, for example, for driving panel-shaped surfaces for the generation of low-frequency sound waves, for example sound waves having a frequencies from 20 Hz. The actuator in accordance with the invention is further suitable for use in vibration suppression systems for the purpose of noise abatement or for the purpose of vibration cancellation in machinery.
The invention also relates to a suspension means constructed and obviously intended for use in a device in accordance with the invention.
With respect to the Claims, it is to be noted that various combinations of characteristic features as defined in the dependent Claims are possible.